The increasing demand for information processing has created the need for many products and services which process and display information. Such products and services typically generate an RF modulated signal suitable for use with an unmodified television set. This has the advantage of reducing the cost of the product or service, since an expensive monitor is not needed. However, the bandwidth limitations of RF modulation for standard TV sets limits the number of characters or alphamosaic symbols that can be legibly displayed on a line to approximately 40. The limitation is especially noticeable on color television sets.
The prior art, typified by U.S. Pat. No. 4,212,008 and U.S. Pat. No. 4,053,878, shows some improvement in the quality of the display when number of characters per line exceeds the limitations imposed by the bandwidth of the display device; however, the prior art is limited and inferior to the present invention in that the prior art cannot greatly increase the number of characters that can be displayed per line. This is especially true for letters, such as lower case "m", that have very high frequency components. What limited reduction of the high frequency component that occurs in some of the prior art requires an expensive double sized, non standard, character generator Read Only Memory.
Techniques for improving the appearance of analog video signals generated by slow scan TV devices are disclosed in the prior art, as typified by U.S. Pat. No. 4,053,931; but such techiques are not applicable for displaying digitally generated alphamosaic symbols, in that such prior art techniques do not decrease the bandwidth of a digitally generated signal, but rather increase it by including a high frequency memory clocking signal in the video output signal. Such memory clocking signals are not normally included as part of a digitally generated character display, and are not introduced into the video signal by the present invention.
Techniques for generating video and keying signals that superimpose self contrasting characters in another video signal are disclosed in the prior art, as typified by U.S. Pat. No. 3,781,849; however, the prior art does not disclose a bandwidth reduction technique suitable for increasing the number of characters per line that can be displayed.
Accordingly, it is an object of the present invention to increase the number of characters or symbols that can be displayed on a line with an unmodified television set.
Another object of the present invention is to reduce the bandwidth of a digitally generated video signal that represents textual information before the video signal is RF modulated, without using any signal other than the video signal.
A further object of the present invention is to decrease the bandwidth of a video signal produced by a standard character generator ROM.
Still another object of the present invention is to allow a 2-level video luminance signal to be transformed to a reduced bandwitdh 2-level video luminance signal.
Still a further object of the present invention is to allow legible display of characters or symbols that have a high frequency component, such as lower case "m".
Still another object of the present invention is to allow bandwidth reduction of the signal from a video generating digital device, which has a memory and a register that indicates the region of the memory being displayed.
Still a further object of the present invention is to allow bandwidth reduction with a novel character generator read only memory.